Photochemical reactions including photo polymerization or photochemical cleavage of molecules in smaller units, as well as optical detection of fluids or components comprised in fluidic substances are well described in the literature and known to those skilled in the art. They are carried out in detecting devices or in reactors having technical size or lab size. Devices for microfluidic applications are known and described. These devices ought to meet the requirements which result from sophisticated techniques:
Optical detection of fluidic samples succeeding to chemical separation or preparation is a most preferred technique since it is applicable without interfering in the chemical system being in the focus. In order to perform such optical detection generally a measuring chamber for the reception of the fluid, a light emitting device and a light receiving device are needed. Performing online detection means designing a measuring chamber as a flow through cell. One may perform transmission or absorption measurements which are corresponding as indicated by optical laws such as Beer's law, which is known to those skilled in the art. Whichever technique is chosen, it presumes guiding light through the sample, accordingly a light path between a light emitting and a light receiving means is required. Simplified, light emitting and light receiving means comprise a light source, detector and the corresponding waveguides. Applying Beer's law furthermore means knowing precisely the geometrical dimensions of the measuring device as far as they are needed to determine optical coefficients such as e.g. extinction. The extinction coefficient refers to the relation of light throughput through a volume of fluid having certain physical and chemical properties. The length of the light path, correlated with said volume of fluid and being correlated with the concentration of the components in the fluid, is accordingly a key parameter in optical detection, being comprised in said extinction coefficient.
The length of the light path is a key parameter in photochemistry, too, since the light throughput frequently determines the yield of a reaction or the conversion: The above cleavage reaction may be performed with an optimal conversion rate if the relation light path-to-reactor volume is optimized, which comprises length of a flow through cell which serves as photo reactor.
A number of microfluidic devices has already been described in the art, the below devices referring on the function of an optical fluidic device as detection device:
A device for microfluidic optical detections is described in U.S. Pat. No. 6,281,975, to Munk. He describes a capillary flow cell with protruding bulb ends providing a high light throughput entrance window for the cell, aiming for an improved sample illumination.
EP 0,089,157 to Le Febre discloses an optical detector cell for determining the presence of a solute in a sample fluid, for the particular application in miniature chromatographic and micro spectroscopic applications. An optical flow path which is parallel to the fluid flow path is provided, allowing maximizing of the sample corresponding to a fixed sample volume, whereby the ability results to measure low threshold concentrations in solutes.
U.S. Pat. No. 4,477,186 to Carlson refers to a photometric cuvette for optical analysis of through flowing media, designed for the measurement of minimum sample amounts.